This helicopter glossary explains the aircraft components, flight controls, aerodynamic principles and operating terms commonly used by pilots, manufacturers and aviation publications. Whether you are learning how helicopters fly or looking up an unfamiliar term, use this guide as a clear introduction to the language of vertical flight.
These definitions are intended for general education and should not replace an approved rotorcraft flight manual, formal instruction or current FAA guidance.
A
Advancing blade
The rotor blade moving in the same general direction as the helicopter’s forward flight. Its airspeed is higher than that of the retreating blade.
Airfoil
A shaped surface that produces an aerodynamic force as air moves around it. Helicopter rotor blades are rotating airfoils.
Angle of attack
The angle between an airfoil’s chord line and the relative wind. It is not the same as blade pitch, although changing pitch often changes angle of attack.
Anti-torque pedals
Foot controls used to vary tail-rotor thrust or another anti-torque system, allowing the pilot to control yaw and counter main-rotor torque.
Articulated rotor
A rotor system whose blades can flap, feather and move fore and aft independently through hinges or flexible components.
Autorotation
A flight condition in which upward airflow through the rotor keeps the blades turning without engine power driving the main rotor. Pilots train to use it during certain power-loss emergencies.
B
Blade flapping
The up-and-down movement of a rotor blade. Flapping helps the rotor compensate for changing aerodynamic forces across the disk.
Blade feathering
Rotation of a rotor blade around its spanwise axis to change blade pitch.
Blade pitch
The angle between a rotor blade’s chord line and the rotor system’s reference plane.
C
Center of gravity
The point at which an aircraft’s total weight is considered concentrated. Helicopters must remain within approved center-of-gravity limits.
Chord line
An imaginary straight line drawn from the leading edge to the trailing edge of an airfoil.
Coaxial rotor
Two main rotors mounted on the same axis and turning in opposite directions, eliminating the need for a conventional tail rotor.
Collective pitch control
The cockpit control that changes the pitch of all main-rotor blades together. It primarily changes rotor thrust and is used to climb, descend and hover.
Compound helicopter
A helicopter supplemented by another source of forward thrust or lift, such as a propeller or wing, while retaining a powered rotor for vertical flight.
Coning
The upward bending or movement of rotor blades into a shallow cone as lift acts against aircraft weight and centrifugal force.
Cyclic pitch control
The cockpit control that changes blade pitch at different points in each rotor revolution, tilting the rotor disk and directing the helicopter’s movement.
D
Density altitude
Pressure altitude corrected for nonstandard temperature. High density altitude reduces rotor, engine and overall helicopter performance.
Disk loading
The helicopter’s weight divided by the area swept by its main rotor. It is one factor affecting hover efficiency and rotorcraft performance.
Dissymmetry of lift
The difference in lift between the advancing and retreating sides of a rotor disk during forward flight. Blade flapping and feathering help compensate for it.
Drag
An aerodynamic force that acts parallel and opposite to the relative wind, resisting an object’s movement through the air.
Dynamic rollover
A rolling motion that can become self-sustaining when a helicopter pivots around a skid, wheel or other point of ground contact beyond a critical angle.
E
Effective translational lift
The improved rotor efficiency that occurs as a helicopter moves into relatively undisturbed air, commonly becoming noticeable during the transition from hover to forward flight.
F
Fenestron
A shrouded tail rotor installed within the vertical tail structure. The term is associated with Airbus helicopter designs.
Flare
A nose-up maneuver used to reduce forward speed and rate of descent, including during the final portion of many autorotations.
Fully articulated rotor
An articulated system, generally with three or more blades, that allows each blade to flap, feather and lead or lag.
G
Ground effect
The increase in rotor efficiency experienced close to the surface as induced airflow and rotor-tip-vortex behavior are altered.
Ground resonance
A potentially destructive vibration involving the rotor and airframe while the helicopter is in contact with the ground, most commonly associated with articulated rotor systems.
H
Helicopter
A rotorcraft that obtains all or a substantial part of its lift from one or more power-driven rotors, allowing vertical takeoff, landing and hovering.
Hover
Flight in which a helicopter maintains a position over a point on the surface at a selected altitude.
Hover in ground effect (HIGE)
A hover close enough to the surface to benefit from ground effect, reducing the power required compared with an out-of-ground-effect hover.
Hover out of ground effect (HOGE)
A hover high enough above the surface that ground effect provides little or no performance benefit.
I
Induced flow
Airflow driven downward through the rotor disk as the rotor produces lift.
L
Lead and lag
The fore-and-aft movement of a rotor blade within the plane of rotation, also called hunting or dragging.
Lift
The component of aerodynamic force acting perpendicular to the relative airflow. The rotor system directs its total aerodynamic force to support and maneuver the helicopter.
Loss of tail-rotor effectiveness (LTE)
An unanticipated yaw rate that may occur when environmental and operating conditions reduce the tail rotor’s ability to provide directional control. It is not necessarily a mechanical failure.
Low-G condition
A condition in which the main rotor is lightly loaded or unloaded. In some helicopter designs, improper control inputs during low-G flight can lead to mast bumping or loss of control.
M
Main rotor
The primary rotating system that produces the aerodynamic force used to lift and control a helicopter.
Mast
The shaft that connects the main-rotor hub to the transmission and transfers power to the rotor system.
Mast bumping
Contact between the rotor hub and mast that can occur in certain teetering rotor systems, particularly following improper control inputs during a low-G condition.
N
Nautical mile
A unit of distance equal to 1,852 meters, approximately 1.151 statute miles. Aviation speeds in knots express nautical miles per hour.
NOTAR
An anti-torque system that uses directed airflow through and around the tail boom instead of a conventional exposed tail rotor. The name means “no tail rotor.”
R
Relative wind
Airflow moving opposite the flight path of an airfoil. For a rotor blade, rotational, induced and aircraft-motion airflow combine to form the resultant relative wind.
Retreating blade
The rotor blade moving opposite the helicopter’s direction of forward flight. Its airspeed is lower than that of the advancing blade.
Retreating blade stall
A high-speed flight limitation that develops when part of the retreating blade can no longer produce the lift required because of excessive angle of attack.
Rigid rotor
A rotor system in which the blades can feather but do not use conventional flapping or lead-lag hinges; flexible components accommodate the necessary movement.
Rotor
A complete system of rotating airfoils, hub and related components that produces aerodynamic force.
Rotor disk
The circular area swept by the tips of the rotor blades as they rotate.
Rotor head
The hub assembly that connects the rotor blades to the mast and allows the movements required by that rotor-system design.
Rotor RPM
The rotational speed of a rotor, expressed in revolutions per minute. Pilots operate within limits specified by the rotorcraft flight manual.
Rotorcraft
An aircraft that uses lift generated by one or more rotors. The category includes helicopters, gyroplanes and other rotor-driven aircraft.
S
Semirigid rotor
A rotor system, commonly with two blades, in which the blades flap together as a unit and can feather individually.
Settling with power
A helicopter performance condition commonly associated with vortex ring state in which powered flight, low forward speed and a substantial descent rate combine to reduce rotor effectiveness.
Swashplate
The control assembly that transfers pilot inputs from the stationary airframe to the rotating rotor blades, changing collective and cyclic pitch.
T
Tail rotor
A rotor mounted near the tail that counters main-rotor torque and provides directional control in many single-main-rotor helicopters.
Tandem rotor
A configuration with two large main rotors mounted one behind the other and rotating in opposite directions.
Teetering rotor
A two-blade semirigid rotor whose blades flap together around a central hinge, much like a seesaw.
Thrust
A force that propels or supports an aircraft. A helicopter changes the magnitude and direction of rotor thrust to hover and maneuver.
Tiltrotor
A powered-lift aircraft with rotors that tilt between vertical lift and airplane-like forward flight. A tiltrotor is rotorcraft, but it is not classified simply as a conventional helicopter.
Torque
The turning force created as the engine drives the main rotor. In a conventional single-main-rotor helicopter, an anti-torque system counters the fuselage’s tendency to rotate the opposite way.
Translating tendency
The lateral drift produced by tail-rotor thrust in many single-main-rotor helicopters. It is also called tail-rotor drift.
Transverse-flow effect
A difference in induced flow between the front and rear portions of the rotor disk during the transition to forward flight, often accompanied by vibration and a tendency to roll.
Turboshaft engine
A gas-turbine engine designed primarily to deliver power through an output shaft, as used to drive the transmission in many helicopters.
U
Uncrewed helicopter
A helicopter designed to operate without an onboard pilot, using remote control, automation or a combination of both. It may also be called an unmanned helicopter.
Useful load
The difference between basic empty weight and gross weight, including items such as crew, usable fuel, passengers and cargo.
V
Vertical takeoff and landing (VTOL)
The capability to take off, hover and land vertically. Helicopters are VTOL aircraft, but not every VTOL aircraft is a helicopter.
Vortex ring state
A hazardous powered-descent condition in which a rotor descends into its own recirculating airflow, reducing lift and increasing the rate of descent.
Y
Yaw
Rotation of the helicopter around its vertical axis, controlled primarily with the anti-torque pedals in a conventional helicopter.
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References and review
Terminology was reviewed against the FAA Helicopter Flying Handbook and its glossary and index. Aircraft-specific procedures and limitations always come from the applicable approved flight manual and qualified instruction.
Last editorial review: September 2026 · Suggest a correction or term